Basic principles that govern the ability of transfection-initiated immunizations to raise immune responses will be addressed using quantitative assays for activities of the cell mediated and humoral arms of the immune system. Studies will be carried out using a murine influenza virus model. Immunizations will be done using pCMV-H1, a DNA expression vector for the H1 influenza hemagglutinin glycoprotein. This glycoprotein has well defined epitopes for antibody, T-helper cell, and cytotoxic T-cell responses. Protection will be tested by lethal challenge via the nares with a mouse adapted form of the A/PR/8/34 (HINI) influenza virus. The first specific aim addresses hoe the form of a DNA- expressed antigen affects access to the immune system by testing the relative efficiency with which cell-associated and secreted forms of H1 raise antibody, cytotoxic T-cell, and protective responses. The second specific aim addresses how different routes of inoculation affect access to the immune system. Experiments in this specific aim will characterize transfection-initiated immune responses raised by intradermal, intranasal, and intravenous administration of DNA. The third specific aim addresses how co-transfected of H1 and lymphokines or a surface marked that costimulates antigen presentation affect the efficiency with which transfected cells access the immune system. These experiments should define basic principles for a novel and highly effective method of presenting antigens to the immune system: direct inoculation of DNA expression vectors. This approach to antigen delivery may also provide a new approach to vaccine development.